Chemical and biological indicators for use in detecting exposure to, and the effectiveness of, oxidizing agents are known in the art. In particular, there are a number of known chemical and biological indicators, with respect to hydrogen peroxide detection and efficacy.
Many chemical indicator compositions include, as one component, an indicator dye. For example, U.S. Pat. No. 6,790,411 to Read discloses a hydrogen peroxide indicator that includes a substrate upon which is disposed an indicator composition that includes at least one of a select group of colorants (dyes) that change color and/or become colorless upon exposure to hydrogen peroxide.
As another example, U.S. Pat. No. 6,063,631 to Ignacio also discloses a sterilization indicator that comprises a substrate and an indicator composition to monitor a sterilization process involving hydrogen peroxide vapor. The indicator composition contains a colorant (dye), such as acid fuchsin, that undergoes a color change upon exposure to hydrogen peroxide. The colorant used may be the sole colorant or, optionally, may be combined with a second colorant that does not change color when exposed to hydrogen peroxide.
Both of the foregoing patents disclose a qualitative assessment of exposure to hydrogen peroxide. Neither of these patents discloses a semi-quantitative chemical indicator composition that shows a dose response to hydrogen peroxide over time, i.e., integrated exposure detection. And, while there are a plethora of dyes that have been used in conventional qualitative chemical indicator compositions (inks), few dyes are suitable for use in a semi-quantitative chemical indicator.
Conventional chemical indicator compositions, comprising traditional known dyes, lack the ability to assess the level of exposure to hydrogen peroxide semi-quantitatively, i.e., achieve a distinctive range of color changes responsive to different doses (concentration x time) of an oxidizing agent, such as hydrogen peroxide. Indicators capable of assessing a predetermined number of exposures (total exposure) to an oxidant-type sterilant are known. For example, two patents to Antonoplos et al., i.e., U.S. Pat. Nos. 6,218,189 and 5,942,438, describe metallic azo dyes used to indicate exposure to an oxidant-type sterilant, including hydrogen peroxide. These two patents do not directly involve integrated exposure evaluation. Both disclose a configuration for the metallic azo dye on a metallic surface of a medical instrument, which will change color only after a predetermined number (total) of exposures to a sterilization process. The change of color of the chemical indicator (azo dyes) serves as a warranty indicator or a limited re-use indicator.
Similarly, U.S. Pat. No. 5,518,927 to Malchesky et al. describes a plastic tag comprising a chemical indicator composition. The tag is attached to an instrument, and after repeated exposures, the chemical indicator composition changes color. Based on the color of the indicator, the total number of sterilizations, i.e., uses, that the instrument has undergone, may be determined.
Neither the Antonoplos et al. nor Malchesky et al. patents are directed to the evaluation of the integrated exposure to an oxidizing agent, such as hydrogen peroxide, using a chemical indicator composition in the setting of a single isolated sterilization process or cycle, so that the dose of hydrogen peroxide to which an article is exposed in one setting can be determined.
U.S. Pat. No. 6,635,439 to Morrison et al. is directed to a method for detecting the integrated exposure to hydrogen peroxide of an article in a sterilization chamber having an atmosphere (including VHP). The method comprises the steps of: (a) placing the item into the chamber; (b) placing a substrate capable of absorbing hydrogen peroxide in the chamber; (c) hydrating the substrate in the presence of a thickening agent; (d) on the substrate, reacting hydrogen peroxide with a dye intermediate and an enzyme capable of reacting with hydrogen peroxide to produce a chromophore indicative of the integrated exposure of hydrogen peroxide in the atmosphere; and (e) correlating the chromophore to the integrated exposure of hydrogen peroxide in the atmosphere. The disclosed and claimed preferred dye intermediate comprises a dye-couple of 3-methyl-2-benzothiazoline hydrazone hydrochloride (MBTH) and 3-dimethylaminobenzoic acid (DMAB). The enzyme is a peroxidase. No traditional chemical indicator dyes are disclosed, and the method does not provide for a quick visual read of hydrogen peroxide exposure.
U.S. Pat. No. 7,186,373 to Centanni discloses a method and apparatus for sensing the concentration of a gaseous sterilant in a sealable enclosure. A chemical indicator composition is provided that changes color when exposed to vaporized hydrogen peroxide (VHP). The chemistry of the indicator is adapted to react when exposed to a specific minimum concentration for a specific minimum period of time. The indicator provides a visual determination of whether articles in a sealable enclosure have been exposed to a minimum threshold of vaporized hydrogen peroxide. The indicator comprises a support strip having individual panels upon which incremental gradients of a chemistry, comprising iodide and thiosulfate, are disposed. Each incremental panel in the strip changes color after a different exposure time to a desired average concentration of vaporized hydrogen peroxide.
There is still a need for a chemical indicator composition that can be used to monitor exposure of articles subjected to a sterilization process employing an oxidizing agent, such as hydrogen peroxide, and to provide not only a qualitative assessment of exposure of exposure to an oxidizing agent, but also a semi-quantitative assessment of the integrated exposure of articles to such oxidizing agent. In addition, there is a need for a chemical indicator composition that provides a convenient visual read-out of the semi-quantitative exposure to oxidizing agents that can be used by persons in the field and that does not require resorting to additional, specialized equipment to “read” absorbance or reflectance of an indicator composition upon exposure.
Accordingly, a useful chemical indicator composition should be able to provide not only a qualitative assessment of exposure to an oxidizing agent, but also a semi-quantitative assessment of the dose of sterilant to which an article has been exposed in a single setting or processing, with the dose being determined by the concentration of sterilant multiplied by the time of exposure, without the need to modify the chemistry of the composition in any way or to utilize integrated concentration gradients of chemistries across various areas of a single support. In short, a chemical indicator composition (ink formulation) is needed, which can be uniformly applied to a support and which comprises an indicator dye that achieves distinctive color changes across a wide range of oxidizing-agent doses, with clear transitions between colors achieved, thus allowing for a semi-quantitative assessment of exposure and a reasonable assessment of whether an effective dose or exposure level has been achieved.
It has been discovered that a colorant (dye), specifically pararosaniline base, also known as parafuchsin, unexpectedly demonstrates distinctly different starting point, intermediate and final endpoint colors during exposure to different doses of hydrogen peroxide vapor under both atmospheric and sub-atmospheric conditions, with clear transitions between the colors achieved from the start of exposure to the final or endpoint of the exposure. Related triphenyl methane dyes, such as acid fuchsin, basic fuchsin and new fuchsin, failed to demonstrate any distinctly different intermediate colors during exposure to varying doses of hydrogen peroxide. As such, these related dyes are not suitable for use in semi-quantitative chemical indicators for hydrogen peroxide vapor, as they show little or no distinctive color changes and no clear transitions between color changes, i.e., between the starting color to the endpoint color, upon exposure to hydrogen peroxide vapor over time.
It is an object of this invention to provide a chemical indicator composition, which is also capable and has the added advantage of providing a semi-quantitative assessment of exposure to an oxidizing agent, such as hydrogen peroxide.
It is another object of this invention to provide a chemical indicator composition for monitoring a sterilization process, such as a process using vaporized hydrogen peroxide as a sterilant, which features a visual read-out of the semi-quantitative exposure of articles subjected to the sterilization process.
It is a further object of this invention to provide a semi-quantitative chemical indicator composition for monitoring a sterilization process, which has the advantage of not requiring modification of the chemistry of the composition, or the application of integrated or gradients of the same chemistry, in order to assess semi-quantitative exposure, when the composition is applied to a single support.
It is a further object of this invention to provide a semi-quantitative chemical indicator composition for determining exposure to an oxidizing agent, such as hydrogen peroxide, which advantageously can be used in the field and does not require any additional specialized equipment to “read” a response.
An advantage of the inventive semi-quantitative chemical indicator composition is that it is easy to manufacture, simple to use and accurate.
Yet another advantage of this invention is a semi-quantitative chemical indicator composition that may be used to determine exposure to an oxidizing agent, such as hydrogen peroxide, in decontamination, disinfection, sanitizing, or other cleaning processes and in environments exposed to such processes.